A communication system may be a facility that enables communication between two or more nodes or devices, such as fixed or mobile communication devices. Signals can be carried on wired or wireless carriers.
An example of a cellular communication system is an architecture that is being standardized by the 3rd Generation Partnership Project (3GPP). A recent development in this field is often referred to as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. E-UTRA (evolved UMTS Terrestrial Radio Access) is the air interface of 3GPP's Long Term Evolution (LTE) upgrade path for mobile networks. In LTE, base stations, which are referred to as enhanced Node Bs (eNBs), provide wireless access within a coverage area or cell. In LTE, mobile devices, or mobile stations are referred to as a user equipment (UE). LTE has included a number of improvements or developments.
LTE-Advanced is an example of a system capable of providing carrier aggregation where a plurality of component carriers are aggregated into an aggregated carrier that has wider transmission bandwidth. When carrier aggregation is used, there are a number of serving cells, one for each component carrier. A primary component carrier (PCC) is provided by a primary cell (PCell) whereas further carriers (secondary component carriers or SCCs) can each be provided by a corresponding secondary cell (SCell). The radio resource control (RRC) connection is handled only by the PCell, served by the PCC. The SCCs may be added and removed as required, while, at least in some cases, the PCC is changed only at handover.
Inter-site carrier aggregation has also been proposed. For example, smaller cells can be used simultaneously in conjunction with a macro cell. An aim of dual connectivity is to decrease mobility related signaling load towards the core network as well as to benefit from gains by the inter-site carrier aggregation. In some aspects dual connectivity may be considered very similar to carrier aggregation with the macro or master serving cell serving as the primary cell and the small cells as the secondary cells.